1. Field of the Invention
The present invention relates to a nitride semiconductor light-emitting diode, and more particularly to a flip chip type nitride semiconductor light-emitting diode having excellent electrical properties and luminance.
2. Description of the Related Art
Recently, a great deal of attention has been directed to nitride semiconductors using nitrides such as GaN, as a photoelectric material and a main core material for electronic devices, since they have excellent physical and chemical properties. In particular, a nitride semiconductor light-emitting diode produces green and blue color light and further light within the UV region, and as a result of technology advancement, has a marked improvement in luminance thereof, therefore it is also applied to full color sign boards, illumination devices, and the like.
Such a nitride semiconductor light-emitting diode is a light-emitting diode to obtain light with a blue or green wavelength and is made of a semiconductor material having the formula of AlxInyGa(1-x-y)N wherein x, y and the sum of x and y are independently between 0 and 1. Nitride semiconductor crystals are grown on a substrate, such as a sapphire substrate, for growing nitride single crystals from a standpoint of lattice matching therebetween. The sapphire substrate is electrically insulative and thus, a final nitride semiconductor light-emitting diode has a structure having both p- and n-electrodes formed on the same surface.
Due to such structural characteristics, the nitride semiconductor light-emitting diode has been actively developed to have a configuration suitable for a flip chip structure. FIG. 1 shows a flip chip type light-emitting device in which a conventional nitride semiconductor light-emitting diode was mounted.
Referring to FIG. 1, the flip chip type light-emitting device; which is designated by reference numeral 20, includes a nitride semiconductor light-emitting diode 10 mounted on a support substrate 21. The nitride semiconductor light-emitting diode 10 includes a sapphire substrate 11, and an n-type nitride semiconductor layer 12, an active layer 13 and a p-type nitride semiconductor layer 14 sequentially laminated thereon. Further, the nitride semiconductor light-emitting diode 10 may be mounted on the support substrate 21 by fusing respective electrodes 19a and 19b on respective lead patterns 22a and 22b via conductive bumps 24a and 24b. In this flip chip structure 20, the sapphire substrate 11 of the light-emitting diode 10 is light-transmissive and thus may be employed as a light-emitting side.
As shown in FIG. 1, an electrode of the flip chip type nitride semiconductor light-emitting diode, particularly a p-electrode, is required to have high reflectivity capable of reflecting light emitted from the active layer 13 toward a light-emitting side while forming ohmic contact with the p-type nitride semiconductor layer 14. Therefore, as shown in FIG. 1, the p-electrode structure may include an ohmic contact layer 15 with high reflectivity formed on the p-type nitride semiconductor layer 14 and a metal barrier layer 16 for preventing diffusion of components of the ohmic contact layer 15.
However, the nitride semiconductor light-emitting diode 10 shown in FIG. 1 has a planar electrode structure. In particular, the p-type ohmic contact layer 15 has a relatively lower resistivity compared to the p-type nitride semiconductor layer 14, and thus electric current crowding occurs, in which a large portion of electric current is concentrated in a region designated by “A” adjacent to the n-electrode, along the ohmic contact layer 15, as shown by arrow.
This electric current crowding not only increases a forward voltage, but also reduces light-emitting efficiency of the active layer spaced relative to the n-electrode, thereby decreasing luminance characteristics thereof. In addition, the region A in which the electric current is concentrated has an increased heat value, thus significantly deteriorating reliability of the diode.